This invention relates to a dry sprinkler system which is of such a size that it is suitable for domestic or small commercial applications.
Systems are presently known which are based upon utilizing dry piping up to the sprinkler head which is filled with water only when required to douse a fire. This type of dry system is used where the system is exposed to temperatures which are liable to drop below freezing which would normally freeze a wet sprinkler system.
The known dry sprinkler systems are, however, built around piping having a minimum diameter of around 21/2 inches, and 21/2 inch clapper valves are used. These clapper valves are held closed by the pressure of air or gas in the dry sprinkler pipes, the air being on one side of a clapper valve and water under pressure being on the other side of the clapper valve. This type of dry system has been in use for about 100 years and the clapper valve has been made of cast iron and although it has been possible to "down size" it to handle a 21/2 inch supply pipe, it cannot be "down sized" any further in its present form and still function satisfactorily. Its high cost also limits its wider application for the protection of the public.
Clapper valves are also affected by water hammer such that if water hammer occurs in the piping system to which the clapper valve and sprinkler system are coupled, the clapper valve will often be jolted open and flood the supply pipes to the sprinklers which will not normally be noticed in operation so that if freezing temperatures occur when the supply pipes are full of water, freezing of the water will cause the sprinkler heads to open or the supply pipes to burst or both.
There has long been a requirement for a satisfactory sprinkler system for use in residential and small commercial units, however wet systems will not be suitable as, for instance, they cannot be used where the piping is in an attic which is outside the insulation of the living areas of the house or when the system serves an unheated area. A wet system is therefore not useable in a bungalow or in the top floor of a house where insulation is laid between and over joists in the standard manner. A dry sprinkler system would appear to be ideal for use in a residential or commerical building where the piping will pass through unheated areas, however it has only been used in commercial installations with piping no smaller than 21/2 inches in diameter. As indicated above, the valves operating this system cannot be "down sized" below 21/2 inches and function effectively.